Ligand-Dependent Chemoselectivity in Gold-Catalyzed Reactions between Anthranils and Diynamides. Formation of Spiro Azacyclic Compounds versus 1-Imino-1H-Indene-3-Carboximidamides

Gold-catalyzed reactions between anthranils and diynamides have been investigated, and their reaction chemoselectivity relies on the types of gold catalysts. With the same anthranil/diynamide mixtures, the use of PPh₃AuCl/AgNTf₂ leads to formation of spiro azacyclic compounds, whereas P(t-Bu)₂(o-biphenyl)AuCl/AgNTf₂ preferably yields 1-imino-1H-indene-3-carboximidamides instead. In the PPh₃AuCl/AgNTf₂ system, an indole intermediate at low temperature for X-ray diffraction study is isolated; this isolable indole species requires anthranil and gold catalyst for efficient formation of spiro azacyclic products. In the case of P(t-Bu)₂(o-biphenyl)AuCl/AgNTf₂, the mechanism of its resulting 1-imino-1H-indene-3-carboximidamides is postulated based on literature reports.